1. Field of the Invention
The present invention relates to an apparatus and method for driving a brushless motor.
2. Description of the Related Art
A typical brushless motor includes a rotor having opposite magnetic poles (N pole and S pole) on its periphery and a stator having a “Y” connection of three coils. The three coils are spaced from each other by 120 degrees, and face the rotor. The N pole of the rotor covers a half surface of the rotor, and the S pole covers the other half of the rotor. If viewed in a cross section of the rotor, the N pole extends 180 degrees of the periphery of the rotor and the S pole extends the other 180 degrees. In order to rotate the brushless motor, the current angular position of the rotor is detected by a magnetic detector (e.g., Hall element), and drive currents are supplied to two of the three coils based on the current angular position of the rotor. Every time the rotor reaches a target angular position, the drive currents are supplied to appropriately selected two coils.
The conventional brushless motor is only able to control the angular position of the rotor at 60-degree intervals. Therefore, if the brushless motor is used in a mechanism to control the angular position of an electronic throttle valve of a vehicle's engine, it is not possible to precisely control the angular position of the electronic throttle valve. Relatively fine (delicate) control of the angular position may be achieved by reducing a rotation ratio of the rotor of the brushless motor by means of a gear train. For instance, the gear train can provide a gear ratio of 0.5 so that the angular position control can be carried out at 30-degree intervals. However, this way of improving the control has a limitation. Accordingly, high precision control cannot be achieved.